1. Field of the Invention
The present invention relates generally to a roller for office automation equipment, and, more particularly, to a developing roller, a charging roller, a transfer roller, a paper feed roller, a de-electricity roller, or a fixing roller used in office automation equipment such as a copying machine, a printer, or a facsimile machine.
2. Description of the Art
A roller for office automation equipment having, for example, a base rubber layer formed on an outer periphery of a shaft thereof, and further, an intermediate layer or a surface layer formed on an outer periphery thereof, has long been used. Conventional materials for forming the above-mentioned base rubber layer have included rubber compositions mainly comprising general-purpose kinds of rubber such as ethylene-propylene-diene terpolymer rubber (EPDM), butadiene rubber, isoprene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, and styrene-butadiene rubber.
However, the aforementioned rubber compositions mainly comprising general-purpose kinds of rubber such as EPDM, while being excellent in terms of material cost, have a defect of being inferior in formability because of a large molecular weight and a low fluidity. Attempts have been made to improve formability by mixing oil in a larger quantity so as to achieve a lower viscosity. Sufficient formability has not as yet been achieved, however, and also there is a defect of a deteriorated compressive permanent strain, one of the properties a roller is required to have. To solve these problems, a liquid rubber composition mainly comprising urethane elastomer or a liquid silicone rubber was proposed and has already been industrialized.
The above-mentioned liquid rubber composition mainly comprising silicone rubber is excellent in formability and provides a high compressive permanent strain property. In contrast, it has a disadvantage in material cost in that liquid silicone rubber is very expensive, and also has a low wear resistance. On the other hand, the above-mentioned liquid rubber composition mainly comprising urethane elastomer, while having the advantages of excellent wear resistance, and a lower material cost as compared with the liquid silicone rubber, has the defect of an insufficient compressive permanent strain property when the hardness of the urethane elastomer is reduced.
In view of these problems, the present applicant has proposed a liquid rubber composition which is derived from at least one of butadiene and isoprene, and mainly comprises a liquid rubber having a structural unit (xcex1) having an alkenyl group on a side chain thereof, and contains a hydrosilyl cross-linking agent and a hydrosilylation catalyst, and suggested use of this liquid rubber composition for various components of office automation equipment (Japanese Patent Application No. 11-74487).
However, in order to use the aforementioned liquid rubber composition as a base rubber layer for a roller in office automation equipment, there is a limit in the degree of freedom in material design by a combination of the molecular weight of the liquid rubber and the cross-linking agent, and the selection of additives is also problematic. Therefore, it is difficult to design a material so as to satisfy hardness, permanent set resistance and reaction stability requirements. Particularly, when adding a softening agent to obtain an appropriate softness, selection of a softening agent may impair a cross-linking reaction or may cause a delay. Mutual solubility and saturation property with a polymer may cause premature separation before the cross-linking reaction, or may cause bleeding (soaking) after the cross-linking reaction.
The present invention was developed in view of the above circumstances, and has an object to provide a roller for office automation equipment which does not impair the cross-linking reaction or does not cause a delay, is excellent in permanent set resistance and low-temperature bleedability, and achieves a lower hardness.
To achieve the above-mentioned object, the roller for office automation equipment according to the present invention comprises a shaft and a base rubber layer formed on an outer periphery of the shaft, wherein the base rubber layer is formed of a liquid rubber composition containing the following constituents (A) to (D):
(A) a liquid rubber, derived from at least one of butadiene and isoprene, and having a structural unit (xcex1) having an alkenyl group on the side chain thereof;
(B) a hydrosilyl cross-linking agent;
(C) a hydrosilylation catalyst; and
(D) a mineral oil containing not more than 0.31 wt. % sulfur.
The present inventors carried out extensive studies so as to satisfy requirements of the base rubber layer of the roller for office automation equipment for the liquid rubber composition proposed by the present applicant. In this process, experiments and studies were conducted to prevent occurrence of bleed in the base rubber layer. As a result, findings were obtained to the effect that a mineral oil was preferable to a synthetic oil. In the process of experiments and studies carried out to improve reaction stability and permanent set resistance, attention was given to the fact that, in the cross-linking reaction of the above-mentioned liquid rubber composition, the alkenyl group present in a molecule in the so-called pendant manner, from among structural units of a specific liquid rubber, serves as a cross-linking site and the hydrosilyl cross-linking agent and the hydrosilylation catalyst exert action on this alkenyl group. That is, attention was directed toward the reaction in which the hydrosilylation catalyst (platinum-based catalyst or the like) is coordinated with the alkenyl group of the liquid rubber, and combines with the hydrosilyl group. Since restriction of the alkenyl group is associated with impairment and delay of the cross-linking reaction, experiments were carried out on materials in the mineral oil which restrict the alkenyl group, bringing about the following findings. The presence of sulfur in the mineral oil in an amount of over 0.31 wt. % impairs the cross-linking reaction, leading to deterioration of material preservation, reaction stability and permanent set resistance. On the basis of these findings, the present inventors found it possible to achieve the desired object by using a liquid rubber composition containing a specific liquid rubber (constituent A), a hydrosilyl cross-linking agent (constituent B), a hydrosilylation catalyst (constituent C), and a specific mineral oil (constituent D), as a material for forming the base layer of the roller for office automation equipment and developed the present invention.
Particularly, when using a naphthene-based oil or a paraffin-based oil as the mineral oil (constituent D), there are a compositions available excellent in photosensitive drum contamination.